Refrigerant compositions

ABSTRACT

Refrigerant composition is disclosed which comprises: (a) pentafluoroethane, trifluoromethoxydifluoromethane or hexafluorocyclopropane, or a mixture of two or more thereof, in an amount of at least 75% based on the weight of the composition, (b) 1,1,1,2- or 1,1,2,2-tetrafluoroethane, trifluoromethoxypentafluoroethane, 1,1,1,2,3,3-heptafluoropropane or a mixture of two or more thereof, in an amount of from 10 to 20% by weight based on the weight of the composition and (c) and ethylenically unsaturated or saturated hydrocarbon, optionally containing one or more oxygen atoms, with a boiling point from −50° C. to +35° C., or a mixture thereof in an amount from 1% to 4% by weight based on the weight of the composition, the weight ratio of component (a): component (b) being at least 4:1.

The present invention relates to refrigerant compositions, particularlylow temperature refrigerants for use in cold stores.

There is a need for a low temperature refrigerant for use in coldstores. Prior to the Montreal Protocol, this function was filled byR502, an azeotrope of R115 and R22. This refrigerant was particularlyattractive in low temperature situations where R12 (CCl₂F) or R22 werereaching their effective working limits. At these low temperatures itwas possible to achieve a significant increase in capacity over thatobtainable with R22 with a major benefit being operation at considerablylower discharge temperatures. However, since R502 contains R115, whichis a strong ozone depleter, it is now no longer available for use.

Subsequently, this requirement has been partially met by using twoblends containing R143a The first is R404A, which consists of R125(44%w/w), R143a (52% w/w) and R134a (4% w/w). The second is R507A, whichconsists of an azeotropic mixture of R125 (50% w/w) and R143a (50% w/w).

The problem with these blends is that they have very high global warningpotentials (GWP).

The concept of a Global Warming Potential (GWP) has been developed tocompare the ability of a greenhouse gas to trap heat in the atmosphererelative to another gas. Carbon dioxide (CO₂) has been chosen as thereference gas. Since GWP's are ratios, they are dimensionless. The GWP'squoted below are those given in IPCC-1995 for 100 year time horizons.The GWP's for blends are calculated by summing the products of the massfraction times the individual component's GWP.

A greenhouse gas is a gas that causes the Earth's atmosphere to trapheat. The greenhouse gas allows the sun's radiation to reach the Earth'ssurface. The Earth's surface is heated by this radiation and emitslonger wavelength intra-red radiation due to the heating. The greenhousegas now prevents this radiation from escaping back into space byabsorbing it and hence traps it in the atmosphere.

R507 has a GWP of 3300 and R404A is only slightly less at 3260. Thesehigh GWP's are due to the presence of R143a Pure R143a has a GWP of 3800compared to that of the other main component, R125, which is only 2800.

R22 alone has also been used, but this is an ozone depleter that will bephased out over the next decade. Also, the efficiency of R22 at the lowtemperatures required for cold storage is poor.

There is now considerable concern about global warming and, hence, it isimportant to use blends with as low a GWP as possible. Clearly there isa need to find a substitute for R502, which is not an ozone depleter,has a low GWP and can operate more efficiently at the low temperaturesrequired than R22, R404A or R507.

According to the present invention there is provided a refrigerantcomposition which comprises:

-   -   (a) pentafluorethane, trifiuoromethoxydifluoromethane or        hexafluoro-cyclopropane, or a mixture of two or more thereof, in        an amount of at least 75% based on the weight of the        composition,    -   (b) 1,1,1,2- or 1,1,2,2-tetrafluoroethane,        trifiuoromethoxypentafluoroethane,        1,1,1,2,3,3-heptafluoropropane or a mixture of two or more        thereof, in an amount of from 5 to 24% by weight based on the        weight of the composition and    -   (c) an ethylenically unsaturated or saturated hydrocarbon,        optionally containing one or more oxygen atoms, with a boiling        point from −50° C. to +35° C., or a mixture thereof, in an        amount from 1% to 4% by weight based on the weight of the        composition, the weight ratio of component (a): component (b)        being at least 3:1.

The percentages quoted above refer, in particular, to the liquid phase.The corresponding ranges for the vapour phase are as follows:

-   -   (a) at least 85%, (b) 2 to 12% and (c) 0.8 to 3%, all by weight        based on the weight of the composition. These percentages        preferably apply both in the liquid and vapor phases.

The present invention also provides a process for producingrefrigeration which comprises condensing a composition of the presentinvention and thereafter evaporating the composition in the vicinity ofa body to be cooled. The invention also provides a refrigerationapparatus containing, as refrigerant, a composition of the presentinvention.

Component (a) is present in an amount of at least 75% by weight based onthe weight of the composition. In practice, the concentration willgenerally be at least 80% by weight with a preferred range of 80 to 90to % by weight, especially 83 to 88% by weight, in particular about 85%by weight. Preferably, component (a) is R125 (pentafluorethane) or amixture containing at least an half, especially at least three quarters(by mass) of R125. Most preferably component (a) is R125 (alone).Generally the cooling capacity of the composition increase withincreasing R125 content; the best cooling capacity and efficiency can beobtained with about 85% R125.

Component (b) is present in the composition in an amount from 5 to 24%by weight based on the weight of the composition. Typically, thecomponent is present in an amount from 7.5% to 20%, generally 10% to15%, by weight, especially about 11.5% by weight. Component (b) ispreferably a mixture containing at least an half, especially at leastthree quarters (by mass) of R134a (1,1,1,2-tetrafluoroethane). Mostpreferably component (b) is R134a (alone).

The weight ratio of component (a): component (b) is at least 3:1,generally at least 4:1, preferably 5:1 to 10:1 and especially 7:1 to9:1.

Component (c) is a saturated or ethylenically unsaturated hydrocarbon,optionally containing one or more oxygen atoms, in particular one oxygenatom, with a boiling point from −50° C. to +35° C. or a mixture thereof.Preferred hydrocarbons which can be used possess three to five carbonatoms. They can be acyclic or cyclic. Acyclic hydrocarbons which can beused include propane, n-butane, isobutane, pentane, isopentane anddimethyl and ethylmethyl ether as well as propane. Cyclic hydrocarbonswhich can be used include cyclo butane, cyclo propane, methyl cyclopropane and oxetan. Preferred hydrocarbons include n-butane andisobutane, with iso-butane being especially preferred. Isobutane isparticularly suited to producing a non-flammable mixture in a worst casefractionation due to a leak.

The presence of at least one further component in the composition is notexcluded. Thus although, typically, the composition will comprise thethree essential components, a fourth component, at least, can also bepresent. Typical further components include other fluorocarbons and, inparticular, hydrofluorocarbons, such as those having a boiling point atatmospheric pressure of at most 40° C., preferably at most 49° C.,especially those where the F/H ratio in the molecule is at least 1,preferably R23, trifluoromethane and, most preferably, R32,difluoromethane. In general, the maximum concentration of these otheringredients does not exceed 10% and especially not exceeding 5% and moreespecially not exceeding 2%, by weight, based on the sum of the weightsof components (a), (b) and (c). The presence of hydrofluorocarbonsgenerally has a neutral effect on the desired properties of theformulation. Desirably one or more butanes, especially n-butane oriso-butane, represents at least 70%, preferably at least 80% and morepreferably at 90%, by weight of the total weight of hydrocarbons in thecomposition. It will be appreciated that it is preferable to avoidperhalocarbons so as to minimise any greenhouse effect and to avoidhydrohalogenocarbons with one or more halogen heavier than fluorine. Thetotal amount of such halocarbons should advantageously not exceed 2%,especially 1% and more preferably 0.5%, by weight.

It has been found that the compositions of the present invention arehighly compatible with the mineral oil lubricants which have beenconventionally used with CFC refrigerants. Accordingly the compositionsof the present invention can be used not only with fully syntheticlubricants such as polyol esters (POE), polyalkyleneglycols (PAG) andpolyoxypropylene glycols or with fluorinated oil as disclosed inEP-A-399817 but also with mineral oil and alkyl benzene lubricantsincluding naphthenic oils, paraffin oils and silicone oils and mixturesof such oils and lubricants with fully synthetic lubricants andfluorinated oil.

The usual additives can be used including “extreme pressure” andantiwear additives, oxidation and thermal stability improvers, corrosioninhibitors, viscosity index improvers, pour point depressants,detergents, anti-foaming agents and viscosity adjusters. Examples ofsuitable additives are included in Table D in U.S. Pat. No. 4,755,316.

The following Examples further illustrate the present invention.

EXAMPLES

Determination of Vapour Pressure/Temperature Relationship for the Blendsto be Tested.

The samples used for testing are detailed in Table 1.

Equipment and Experimental

The equipment used for determining the vapour pressure/temperaturerelationship consisted of a 1 litre Parr reactor immersed completely ina thermostatically controlled water bath. The bath temperature wasmeasured using a calibrated platinum resistance thermometer with anIsotech TTI1 indicator. The resolution of the thermometer is 0.01° C.The pressure (press) was read with a calibrated pressure transducer withan experimental accuracy of 0.01 bara and read on a Druck DR1instrument.

Approximately, 1.2 kg of the refrigerant was charged into the Parrreactor. The reactor was then cooled overnight. When it had reachedtemperature, the pressure and temperatures were recorded every tenminutes until constant.

The data obtained does not give the dew point and hence does not givethe glide. An approximate evaluation of the glide can be obtained byusing the REFPROP 6 program. The relationship of the glide to the bubblepoint is usually nearly linear and can be represented by a linearequation. In the case of R407C, a binomial equation had to be used.These equations can now be used to give an approximate glide for theexperimentally determined bubble points. This is effectively anormalisation of the calculated glide to the experimentally determineddata. The pressure of the dew point can now be approximated by applyingthe relationship for temperature/pressure, which was found for thebubble point. The glide equations obtained are also shown in Table 2.These equations can now be used to obtain vapour pressure/temperaturetables.

Determination of the Performance of the Refrigerants on the LowTemperature (LT) Calorimeter.

Equipment and General Operating Conditions

The performance of the refrigerants was determined on the lowtemperature (LT) calorimeter. The LT calorimeter is fitted with a Bitzersemi-hermetic condensing unit containing Shell SD oil. The hot vapourpasses out of the compressor, through an oil separator and into thecondenser. The discharge pressure at the exit of the compressor is keptconstant by means of a packed gland shut-off valve. The refrigerant thentravels along the liquid line to the evaporator.

The evaporator is constructed from 15 mm Cu tubing coiled around theedges of a well insulated 32 litre SS bath. The bath is filled with50:50 glycol:water solution and heat is supplied to it by 3×1 kW heaterscontrolled by a PID controller. A stirrer with a large paddle ensuresthat the heat is evenly distributed. The evaporating pressure iscontrolled by an automatic expansion valve.

The refrigerant vapour returns to the compressor through a suction lineheat exchanger.

Twelve temperature readings, five pressure readings, compressor powerand heat input are all recorded automatically using Dasylab.

The tests were run at a condensing temperature of 40° C. and anevaporator superheat of 8° C. (±0.5° C.).

For R22 the temperature at the end of the evaporator was maintained at8° C. above the temperature equivalent to the evaporating pressure.

For the other refrigerants the temperature at the end of the evaporatorwas maintained at 8° C. above the temperature equivalent to theevaporating pressure (Dew point)

The mean evaporator temperature (ev. temp) for these refrigerants wascalculated by taking the temperature equivalent to the evaporatorpressure from the bubble point table and adding to that half the glideat that temperature.

Initially, the pressure was roughly set and then the temperature of thebath was set. The pressure would then be readjusted to ensure that therewas 8° C. superheat present. The superheat was measured from the thirdevaporator outlet. No adjustments were made during the run, except forpossibly minor changes to the valve at the exit of the compressor, inorder to keep the conditions as constant as possible. The test was thencontinued for at least one hour during which time 6 readings were takeni.e. every 10 minutes. If these readings were stable, then their averagewas calculated.

Specific Experimental Details for Each Refrigerant

The refrigerant list is given in the order in which the measurementswere carried out.

R22: R22 (3.477 kg) was charged into the liquid receiver. Since this wasthe first time that the LT calorimeter had been used since a majormodification base data for R22 was required. Accordingly, eight datapoints were obtained between the evaporating temperatures of −33° C. to−21° C.

75%, R125: Approximately 3.54 kg were charged into the liquid receiver.Four data points were obtained between the mean evaporating temperaturesof −31° C. to −23° C. respectively. At a mean evaporating temperature of−23° C. the expansion valve was fully opened.

85% R125: Approximately 3.55 kg were charged into the liquid receiver.Four data points were obtained between the mean evaporating temperaturesof −31° C. and −25° C. At a mean evaporating temperature of 26° C. theexpansion valve was fully opened.

85% R125 (R600a): Approximately 3.56 kg were charged into the liquidreceiver. Five data points were obtained between the mean evaporatingtemperatures of −44.5° C. and −28° C.

R407C: Approximately 3.59 kg were charged into the liquid receiver. Fivedata points were obtained between mean evaporating temperatures of −32°C. to −20° C.

70% R125: Approximately 3.5 kg were charged into the liquid receiver.Five data points were obtained between the mean evaporating temperaturesof −32° C. to −21° C.

R404A: Approximately 3.51 kg were charged into the liquid receiver. Fivedata points were obtained between the mean evaporating temperatures of−33° C. to −25° C.

Results

The results obtained are summarised in Tables 3-8. Mean Ev. Temp=Meanevaporation temperature; Air On Condenser=temperature of the air in theroom that is blown over the air cooled condenser, measured just prior tothe air blowing over the condenser; Press=pressure.

Comments and Discussion on the Experimental Results

Graph 1 shows a comparison of capacities at a mean evaporatingtemperature of −30° C., compared to R404A. This evaporating temperatureis considered to be fairly typical of where a low temperaturerefrigerant would be expected to operate. It can be seen that 85% R125and 85% R125 (R600a) have a slightly better relative capacity thanR404A, whereas the other refrigerants tested are poorer. R22 and 75%R125 are the next best. At this temperature R407C is the poorest, but itimproves relatively as the mean evaporating temperature increases.Generally, there is an improvement in cooling capacity as the R125content increases.

Graph 2 shows the COP results obtained. It shows that 85% R125 and 85%R125 (R600a) give the best efficiency at −30° C. and are the onlyrefrigerants better than R404A.

Graphs 3 and 4 show the capacity and COP for any given refrigerantrelative to R22. These again show the similarity of 85% R125 and 85%R125 (R600a) to R404A, which are all 5-10% up on R22.

The preferred formulations are therefore 85% R125 and 85% R125 (R600a).Assuming that n-butane and isobutane have the same GWP as methane (21).This is 22% less than that of R404a and 23% less than that of R507.

The preferred compositions are 85% w/w R125, 11.5% w/w R134a and 3.5%w/w butane or isobutane. These have a vapour pressure-temperaturerelationship very close to that of R404A. For example, at −30° C. theR404A liquid has a vapour pressure of 0.209 MPa (30.3 psia) and thepreferred compositions have a vapour pressure above the liquid of 0.218MPa (31.6 psi) for butane and 0.223 MPa (32.3 psia) for isobutane i.e.only 46% higher. TABLE 1 Details of test refrigerants DescriptionComposition 70% R125 R125/134a/600 (70.0/26.5/3.5) 75% R125R125/134a/600 (75.0/21.5/3.5) 85% R125 R125/134a/600 (85.0/11.5/3.5) 85%R125 (R600a) R125/134a/600a (85.0/11.5/3.5) R407C R32/125/134a(23.0/24.0/52.0) R404A R125/143a/134a (44.1/51.9/4.0)

TABLE 2 Results of the experimental SVP measurements and the glide fromREFPROP6 SVP equation Description (see note 1) Glide equation (see note2) 70% R125 y = −2357.53678x + y = −0.02391x + 3.22225 13.02249 R2 =0.99786 75% R125 y = −2318.71536x + y = −0.02122x + 2.84478 12.93301 R²= 1.00000 R² = 0.99704 85% R125 y = −2318.35322x + y = −0.01305x +1.85013 12.98687 R² = 0.99998 R² = 0.99456 85% R125 y = −2307.282362x +y = −0.0157x + 1.7337 (R600a) 12.964359 R² = 0.998 R² = 0.999973 R407C(3) y = −2422.08237x + y = −0.000118x2 − 0.027343x + 13.27060 6.128020R² = 0.998575 R404A y = −2367.62611x + y = −0.005014x + 0.54712513.14935 R² = 0.99994 R² = 0.995941 R22 (see note 4) Not applicableNotes:(1) In this equation x = 1/T where T is the bubble point in Kelvin: y =ln(p), where p is the saturated vapour pressure in psia(2) In this equation x = t, where t is liquid temperature (bubble point)in degree C. and y = glide in deg C. at the bubble point temperature.(3) The data used was from Refprop, but was in agreement with that fromthe Ashrae handbook and from ICI.(4) The vapour pressures for R22 were obtained from the Ashrae handbookby intepolation.

TABLE 3 R22 CONDENSING AT 40° C. IN LT-CALORIMETER Evaporator MeanDischarge absolute Evap Capacity Ev. Discharge Air On absoluteCondensing inlet Temp Evap Temp Compressor (Heat input Evap. Temp TempCondenser Press (MPa) Temp Press (MPa) BUBBLE DEW Power kwh kwh) C.O.P.Superheat −33.0 159.5 24.2 1.532 40.0 0.144 −33.0 −33.0 1.339 1.224 0.918.5 −30.2 153.1 18.9 1.545 40.3 0.163 −30.2 −30.2 1.412 1.367 0.97 8.5−27.8 152.4 20.6 1.538 40.1 0.180 −27.8 −27.8 1.486 1.653 1.11 8.5 −27.5156.6 24.4 1.516 39.5 0.182 −27.5 −27.5 1.482 1.704 1.15 7.7 −25.4 155.624.3 1.547 40.4 0.199 −25.4 −25.4 1.606 2.020 1.26 8.4 −25.0 155.2 24.21.538 40.1 0.205 −25.0 −25.0 1.660 2.139 1.29 8.8 −22.5 154.5 26.3 1.55140.5 0.223 −22.5 −22.5 1.686 2.323 1.38 7.9 −20.7 150.5 24.7 1.555 40.60.238 −20.7 −20.7 1.729 2.526 1.46 8.1Note:All temperatures are in ° C.

TABLE 4 70% R125 (69.98% R125/26.51% R134a/3.51% R600) CONDENSING AT 40°C. IN LT-CALORIMETER (ITS 7694) Evaporator Mean Discharge absolute EvapCapacity Ev. Discharge Air On absolute Condensing inlet Temp Evap TempCompressor (Heat input Evap. Temp Temp Condenser Press (MPa) Temp Press(MPa) BUBBLE DEW Power kwh kwh) C.O.P. Superheat −32.4 117.7 23.4 1.69740.5 0.160 −34.4 −30.4 1.302 1.148 0.88 8.3 −29.6 115.6 24.8 1.690 40.30.180 −31.6 −27.6 1.384 1.389 1.00 7.9 −26.1 108.8 21.2 1.686 40.2 0.207−28.1 −24.2 1.499 1.768 1.18 8.0 −23.5 108.1 23.4 1.691 40.3 0.230 −25.4−21.6 1.589 2.046 1.29 8.2 −21.5 107.3 24.4 1.691 40.3 0.248 −23.4 −19.61.657 2.260 1.36 8.0Note:All temperatures are in ° C.

TABLE 5 75% R125 (75.02% R125/21.48% R134a/3.50% R600) CONDENSING AT 40°C. IN LT-CALORIMETER (ITS 7616) Evaporator Mean Discharge absolute EvapCapacity Ev. Discharge Air On absolute Condensing Inlet Temp Evap TempCompressor (Heat input Evap. Temp Temp Condenser Press (MPa) Temp Press(MPa) BUBBLE DEW Power kwh kwh) C.O.P. Superheat −30.7 115.2 25.0 1.73640.0 0.187 −32.4 −28.9 1.421 1.403 0.99 8.1 −27.8 112.4 25.7 1.746 40.30.210 −29.5 −26.0 1.476 1.644 1.11 7.7 −25.0 110.9 28.1 1.733 39.9 0.234−26.7 −23.3 1.610 1.981 1.23 7.6 −23.3 108.0 26.7 1.731 39.9 0.250 −25.0−21.6 1.653 2.190 1.33 7.6Note:All temperatures are in ° C.

TABLE 6 85% R125 (85.05% R125/11.45% R134a/3.50% R600) CONDENSING AT 40°C. IN LT-CALORIMETER (ITS 7677) Evaporator Mean Discharge absolute EvapCapacity Ev. Discharge Air On absolute Condensing inlet Temp Evap TempCompressor (Heat input Evap. Temp Temp Condenser Press (MPa) Temp Press(MPa) BUBBLE DEW Power kwh kwh) C.O.P. Superheat −31.4 109.3 20.3 1.83940.1 0.197 −32.6 −30.3 1.462 1.501 1.03 8.1 −28.7 109.8 22.6 1.844 40.20.219 −29.8 −27.6 1.567 1.724 1.10 8.4 −26.6 107.2 23.1 1.823 39.7 0.238−27.7 −25.5 1.626 1.970 1.21 7.8 −25.2 103.9 20.4 1.845 40.2 0.251 −26.3−24.1 1.688 2.190 1.30 8.2Note:All tempuratures are in ° C.

TABLE 7 R407C (23.02% R32/25.04% R125/51.94% R134a) CONDENSING AT 40° C.IN LT-CALORIMETER (ITS 7361) Evaporator Mean Discharge absolute EvapCapacity Ev. Discharge Air On absolute Condensing inlet Temp Evap TempCompressor (Heat input Evap. Temp Temp Condenser Press (MPa) Temp Press(MPa) BUBBLE DEW Power kwh kwh) C.O.P. Superheat −32.4 135.3 19.8 1.73539.7 0.147 −35.9 −28.9 1.287 0.974 0.76 7.6 −29.4 133.8 18.9 1.738 39.70.167 −32.9 −26.0 1.428 1.405 0.98 7.7 −25.7 132.4 20.1 1.746 39.9 0.196−29.1 −22.3 1.499 1.736 1.16 7.8 −23.0 130.8 20.8 1.733 39.6 0.218 −26.4−19.6 1.650 2.190 1.33 7.6 −19.6 129.0 22.5 1.761 40.3 0.250 −22.9 −16.21.774 2.649 1.49 8.0Note:All temperatures are in ° C.

TABLE 8 R404A (44% R125/52% R143a/4% R134a) CONDENSING AT 40° C. INLT-CALORIMETER (ITS 7726) Evaporator Mean Discharge absolute EvapCapacity Ev. Discharge Air On absolute Condensing inlet Temp Evap TempCompressor (Heat input Evap. Temp Temp Condenser Press (MPa) Temp Press(MPa) BUBBLE DEW Power kwh kwh) C.O.P. Superheat −33.0 123.4 23.7 1.83139.7 0.182 −33.4 −32.7 1.405 1.291 0.92 8.0 −31.2 120.5 23.1 1.829 39.70.196 −31.5 −30.8 1.472 1.473 1.00 7.6 −29.6 118.1 22.8 1.824 39.6 0.210−29.9 −29.2 1.522 1.624 1.07 7.7 −26.9 118.2 25.1 1.850 40.1 0.233 −27.3−26.6 1.641 1.910 1.16 8.1 −24.7 112.6 21.4 1.865 40.5 0.254 −25.0 −24.31.740 2.272 1.31 8.1Note:All temperatures are in ° C.

TABLE 9 85% R125 (R600a) (85% R125/11.45% R134a/3.50% R600a) condensingat 40° C. in LT-Calorimeter Mean Discharge Evaporator Evap Ev. DischargeAir On Press Condensing Inlet Press Temp Evap Temp Compressor CapacityEvap. Temp Temp Condenser (psig) Temp (psig) BUBBLE DEW Power kwh (kW)C.O.P. Superheat −44.5 115.4 24.5 256.0 40.2 2.0 −45.8 −43.3 1.022 0.3130.31 8.5 −39.9 116.6 24.6 254.7 40.0 5.8 −41.1 −38.7 1.137 0.623 0.557.9 −36.2 114.2 21.8 254.2 39.9 9.3 −37.3 −35.0 1.319 1.025 0.78 8.3−31.8 107.4 19.1 251.6 39.5 14.1 −32.9 −30.7 1.462 1.482 1.01 8.5 −28.0106.5 20.8 254.0 39.9 18.8 −29.1 −26.9 1.605 1.827 1.14 8.3 −24.0 101.819.7 253.5 39.8 24.4 −25.0 −22.9 1.763 2.336 1.33 7.9

1. A refrigerant composition which comprises: (a) pentafluoroethane,trifluoromethoxydifluoromethane or hexafluorocyclopropane, or a mixtureof two or more thereof, in an amount of at least 75% based on the weightof the composition, (b) 1,1,1,2- or 1,1,2,2-tetrafluoroethane,trifluoromethoxypentafluoroethane, 1,1,1,2,3,3-heptafluoropropane or amixture of two or more thereof, in an amount of from 5 to 24% by weightbased on the weight of the composition and (c) an ethylenicallyunsaturated or saturated hydrocarbon, optionally containing one or moreoxygen atoms, with a boiling point from −50° C. to ±35° C., or a mixturethereof, in an amount from 1% to 4% by weight based on the weight of thecomposition, the weight ratio of component (a): component (b) being atleast 3:1.
 2. A composition according to claim 1 in which component (c)is present in an amount from 3 to 4% by weight based on the weight ofthe composition.
 3. A composition according to claim 2 in whichcomponent (c) is present in an amount of about 3.5% by weight based onthe weight of the composition.
 4. A composition according to claim 1 inwhich component (c) is one or more of propane, n-butane, isobutane,cyclobutane, cyclopropane, methylcyclopropane, pentane, isobutane,dimethylether, ethylmethyl ether, propene and oxetan.
 5. A compositionaccording to claim 4 in which component (c) is n-butane and/orisobutane.
 6. A composition according to claim 1 wherein (a) ispentafluoroethane.
 7. A composition according to claim 1 in whichcomponent (a) is present in an amount from 80 to 90% by weight based onthe weight of the composition.
 8. A composition according to claim 7 inwhich component (a) is present in an amount from 83 to 88% by weightbased on the weight of the composition.
 9. A composition according toclaim 1 in which component (b) is 1,1,1,2-tetrafluoroethane.
 10. Acomposition according to claim 1 in which component (b) is present in anamount from 10 to 15% by weight based on the weight of the composition.11. A composition according to claim 1 in which the weight ratio ofcomponent (a): component (b) is 5:1 to 10:1.
 12. A composition accordingto claim 11 in which the weight ratio is 7:1 to 9:1.
 13. A compositionaccording to claim 1 which comprises a further component.
 14. Acomposition according to claim 13 in which the further component is ahydrofluorocarbon.
 15. A composition according to claim 14 in which thehydrofluorocarbon has a boiling point at atmospheric pressure of at most−40° C.
 16. A composition according to claim 14 in which the F/H ratioin the hydrofluorocarbon is at least
 1. 17. A composition according toclaim 16 in which the hydrofluorocarbon is difluoromethane ortrifluoromethane.
 18. A composition according to claim 13 in which thefurther component is present in an amount not exceeding 5% by weightbased on the weight of (a), (b) and (c).
 19. A composition according toclaim 18 in which the further component is present in an amount notexceeding 2% by weight based on the weight of (a), (b) and (c). 20-21.(canceled)
 22. A process for producing refrigeration which comprisescondensing a composition as claimed in claim 1 and thereafterevaporating the composition in the vicinity of a body to be cooled. 23.A refrigeration apparatus comprising, as refrigerant, a composition asclaimed in claim 1.